To make partner at a big law firm is to grab a brass ring of prestige, wealth and security.

Now, for some partners, however, that ring is being yanked away.

Wrestling with a difficult market, some big law firms are demoting partners — meaning they are no longer owners in the firm who share in annual profits.

The latest to publicly weigh such a step is Shearman & Sterling, a powerhouse New York firm that indicated recently that it would revamp itself, primarily through demotions and delays in promotions to full partnership status.

Demoting, or even cutting, partners is not new in the legal industry. A decade ago, the efforts at Shearman & Sterling to jettison unproductive partners were called “Shearminations.” But it is a tool the legal industry once wielded sparingly.

“It’s back now because there is a growing recognition that demand for legal services is not picking up and firms are facing overcapacity issues,” said Peter Zeughauser, a law firm consultant.

Some firms have been quietly weeding their partner ranks as a result. In a process called de-equitizing, law firms set retirement dates for certain equity partners or reduce them to salaried status, cutting them out of the yearly profit distribution.

Such demotions take a heavy toll personally and financially.

One lawyer, who graduated from an Ivy League law school in 1994, recalled that her own experience was dismaying and disorienting. After a decade of law firm and government work, she made partner at an elite firm but was nudged out the door a few years later. It was, she said, the first negative feedback she had received from her fellow partners.

A feeling of loss stuck with her after her exit, she said.

The lawyer said that she had to start her career over, taking a job that was more junior and at lower pay. She agreed to tell her story on the condition that she and her former firm not be identified, fearing that her professional reputation and livelihood would be seriously harmed as a result.

Not all de-equitized lawyers leave. The number of nonequity partners at the 200 largest law firms in the country has more than tripled to an average of 117 per firm in 2014 from an average of just 35 in 1999, said James D. Cotterman, a principal at Altman Weil, a legal consulting firm.

And not all nonequity partners are the result of reductions in rank. Some lawyers choose it so they do not have to invest capital in the firm — typically in the hundreds of thousands of dollars — or risk partnership liability if someone sues the firm. And more appear to settle for it as the top level of their career.

In 2014, nonequity partners made up slightly more than 40 percent of all partners at premier firms, up from 17 percent a decade and a half ago.

This year, 22 percent of the 93,000 lawyers in the top 100 firms are equity partners, Mr. Cotterman said, compared with 35 percent in 1996.

Those who have reached the top rank, at least at big law firms, work more hours than their lower-ranked colleagues, according to figures from Citi Private Bank’s Law Firm Group. Last year, ownership partners worked an average of 87 hours annually more than nonequity partners — up from 64 hours more five years ago, according to a sample of 40 of the largest 50 firms.

Putting lower-performing colleagues out on the sidewalk, or even packing them off to a smaller office, is not easy. And firms are loath to draw attention to such moves for fear of damaging their prestige and their ability to attract new business.

“In too many firms,” according to a study by Altman Weil, “personal, political and cultural obstacles are hindering pragmatic economic decisions,” including ousting lawyers who are not needed or not attracting lucrative legal work.

Still, the winnowing of partners — who can take home hundreds of thousands or even millions of dollars in annual compensation — is taking place more frequently.

At Shearman, the decision to revamp its partnership was put in motion a few weeks ago while the firm was in the public eye, advising a client, the board of Wells Fargo, on handling the scandal over the creation of millions of unauthorized customer accounts.

Even as the firm’s lawyers were doling out legal advice to the banking giant’s directors, partners were weighing how “to create a more efficient practice group management structure,” according to emails reported by legal publications.

The ensuing departure of senior partners amplified attention around the firm’s actions, but Shearman provided only sparse details of its plan.

“We are not doing interviews about changes to our partnership structure,” said Amy Malsin, a spokeswoman for the firm, but she noted that Shearman regularly reviewed “how and where we invest equity and manage head count.”

Founded more than a century ago, Shearman found early success tying itself to Wall Street. It later enhanced its reputation by helping Ford Motor go public in 1956 and, in 2006, advising Pixar during its acquisition by Disney. The firm has had its ups and downs, though, with belt-tightening, including layoffs in the early 2000s, but it bounced back.

The latest push for an overhaul at Shearman came after a raft of prominent partners, including an antitrust specialist with the blue-chip client Qualcomm, left the firm. Another clutch of partners specializing in mergers and acquisitions decamped to a rival firm.

Like some competitors in its tier, Shearman has struggled to grow of late. Its average profit per equity partner fell almost 4 percent last year, to just under $1.85 million. And gross revenue last year grew less than 2 percent, to $860.5 million.

Even so, this year the firm moved up two places, to No. 25, on the American Lawyer 2016 ranking of top firms, a status that is bestowed on firms with strong pro bono programs, diversity in their ranks and high associate satisfaction scores.

Last year, Shearman had 162 equity partners and 26 nonequity, or fixed share, partners among its nearly 840 lawyers.

The changes will go “into effect by the year end,” said Ms. Malsin, the firm’s spokeswoman. The existing layer of nonequity partners will be expanded “to allow junior partners to grow into equity partnership,” she added.

At some law firms, including Shearman, it is difficult to sever partners because a majority of partners is needed to take such action. Even so, at Shearman and some other firms, it is possible to de-equitize partners without their consent. Even without that cudgel, the firm can cut back equity partner compensation as much as 25 percent annually — a brusque sign that it is time to leave.

The advent of a large class of nonequity partners bolsters the firm’s income but could further expand the firm’s bulging middle ranks — those who are above associates but below full-fledged partners.

Until that rotund middle is reduced, Mr. Cotterman of Altman Weil said, nonequity partners will not be anomalies.

“With law firms having to add 5 percent to 15 percent in new business each year just to stay even,” he said, all law firms are going to have to slim down “in some form.”

Correction:

An article on Tuesday about overhauls at some big law firms that include reductions in the number of partners misstated the circumstances of some departures at Shearman & Sterling that preceded structural changes there. An antitrust specialist with Qualcomm as a client left, not three strategists whose clients also included Viacom. (Two of those strategists did not leave the firm, but went to another office.)

A version of this article appears in print on , on Page B1 of the New York edition with the headline: Law Firms Cull Partner Ranks in Face of Market Challenges. Order Reprints | Today’s Paper | Subscribe